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Cake day: July 6th, 2023

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  • P(failure second try)=(2/3)^2 since you can eliminate one choice but 2 others are still wrong.

    To total:
    P(failure)=(3/4)2*(2/3)2=1/4
    1-1/4=0.75

    So the probability of passing is 0.75

    Edit:
    Remark: this problem is elegant if you attempt to calculate the passing as the complement of failure rather than enumerate all successes. Shouldn’t take more than 3 minutes with a clear head if you know the correct approach. If this was an college level intro probability exam question, it should be done the fast way since it’s meant to eat up your time otherwise.